Intermolecular and intramolecular forces
Intermolecular forces hold molecules and/or compounds (in the case of ionic bonds) to each other, while intramolecular forces binds atoms to form a molecule or formula unit. Intramolecular forces Ionic bond The shared electron that occurs between two atoms with an electronegativity difference greater than 1.7 defines ionic compounds and is the strongest form of intramolecular bonds. Unlike covalent bonding where electrons are shared between atoms, there is a complete transfer of electrons in ionic bonding. These types of bonds usually occur between metals and non-metals where the metals donate electrons to the non-metal. Covalent bonding This type of bond usually forms between two non-metals and can be either polar or non-polar depending on the difference in electronegativity. If the difference is above 0.5 it is considered polar, if it is less, it is non-polar. Since the difference in electronegativity is not large enough, electrons are not transferred like in ionic compounds, but they are shared between the atoms. A polar covalent bond creates a bond dipole in which one side is partially negative while the other is partially positive. Covalent bonds are strong, but not as strong as ionic bonds. Polar covalent bonds are stronger than non-polar covalent bonds because there is a stronger attraction between the atoms. Some compounds (known as covalent networks) are formed by many intramolecular covalent bonds. They include diamond, graphite, silicon dioxide. Metallic bonding Metallic bonds arise when metal atoms share electrons with one another. The electrons become delocalised and float freely from one atom to the next, filling several orbits. This bond is quite strong. Intermolecular forces Dipole-dipole atttraction When two individual molecules have molecular dipoles, the positive end of one will be attracted to the negative end of the other. This force is intermediate in strength. Hydrogen bonding A form of dipole-dipole attraction between hydrogen and a "hydrogen bond donor", which is an electronegative atom either''' fluorine',' oxygen',' or '''nitrogen. The hydrogen will serve as the positive end of the dipole and be attracted to the donor atom of nearby molecules. This is stronger than the dipole-dipole force. Ion Dipole A form of dipole attraction between a molecule with a molecular dipole and an ion. The ion is attracted with the opposite charge of the dipole. This is the strongest dipole intermolecular force. Dispersion force (Van der Waals) In otherwise unbonded solutions, the electrons of the substances will orbit randomly and eventually develop a weak dipole, simply by having more electrons on one side than another. This negative end of the dipole will attract electrons in surrounding atoms, creating a cascade of weakly interacting atoms or molecules bound by London dispersion forces. Ion-induced dipole In the presence of a positive or negative ion, the electrons of an otherwise neutral atom will be attracted by a positive atom or repelled by a negative atom. Either way, there is an uneven distribution of electrons within the induced atom, creating a temporary dipole. This dipole can cause other nearby neutral atoms to form dipoles as well. Dipole-induced dipole Similar to ion-induced dipoles, they are dipoles whose polarity arises in the presence of an existing dipole. Ranking of purely intermolecular forces Ion-dipole > Hydrogen Bond > Dipole-Dipole > Ion-induced dipole > Dipole-induced dipole > London dispersion Category:Chemistry